On Mon, 19 May 2014 12:19:47 -0400 Gary Dale <garydale@torfree.net> wrote: > On 19/05/14 09:04 AM, Henrique de Moraes Holschuh wrote: > > On Mon, 19 May 2014, Gary Dale wrote: > >> This led me into partitioning. I thought that GPT pretty much gave > >> you proper partition alignment, but now I think I was mistaken on > > Unfortunately, it doesn't :-( > > > >> that point. gdisk shows my first partition starting at 34, with the > >> fdisk info showing 255 heads, 63 sectors/track. That doesn't come > >> close to 4k alignment. > > You're using a SSD. You need 4KiB aligment, but you really want > > erase-block alignment. When in doubt, use the 1MiB default > > alignment used by Debian (and most other Linux distros) and also by > > MS Windows. > > > > Since Debian Wheezy, the Debian installer for x86 (i386 and amd64) > > should have done this properly as long as you let it wipe any > > preexisting partition tables (that might be incorrectly aligned). > > > > Unfortunately, the Debian installer for other arches (such as > > powerpc) may be buggy and get it wrong (in fact, powerpc's > > installer fails to align GPT partitions). > > > > BTW: you also need to align the data area of any LVM PVs (which > > really can only be done at PV creation time), and create the > > filesystem with the proper alignment for their internal > > structures. The debian installer for i386 and amd64 is known to do > > this correctly, but YMMV on any of the other arches. > > > >> Before I haul out sysrescuecd and move my partitions around, I > >> thought I'd ask for suggestions. Should I move the filesystem to > >> something that is a multiple of 8, do something else, or look > >> elsewhere for a solution to my problem? > > Align everything to 1MiB (or, if you happen to know it, the erase > > block size of your SSD, which will be a submultiple of 1MiB). > > > > You can ignore cylinder alignment: the BIOS would boot using LBA > > information anyway and ignore the cylinder/sector/head crap, EFI > > will grok the GPT natively, and you should not be letting any > > operating systems old enought to not operate in LBA mode anywere > > close to a raw device. > > > > Don't use half-assed tools to mess with the partitions. Proper > > tools known to get aligment right by default on Debian > > stable/testing are: gdisk, cfdisk, mdadm, lvm, mke2fs (mkfs.ext4), > > mkfs.xfs (for XFS). "parted" gets it right only if you give it > > fuzzy units (such as "0%" instead of "0" for the start of a > > partition). fdisk also aligns correctly when it is not trying to > > be compatible with old DOS. > When I use gparted with 1M alignment, it didn't change the 34 start > sector. In fact the only change was that gdisk now reports 2-sector > alignment: > > Found valid GPT with protective MBR; using GPT. > Disk /dev/sda: 234441648 sectors, 111.8 GiB > Logical sector size: 512 bytes > Disk identifier (GUID): 8017C70A-FA69-48DD-9227-825774B31816 > Partition table holds up to 128 entries > First usable sector is 34, last usable sector is 234441614 > Partitions will be aligned on 2-sector boundaries > Total free space is 911 sectors (455.5 KiB) > > Number Start (sector) End (sector) Size Code Name > 1 34 232343551 110.8 GiB 8300 Linux > filesystem 2 232343552 234440703 1024.0 MiB EF02 > > I then tried it by putting 1M free in front of the first partition. > This changed the start sector to 4096, which is definitely on a 4k > boundary, if slightly wasteful. This confirms your point that parted > is somewhat flaky when dealing with alignments. While slightly wasteful, in practice you don't want to fill up an SSD anyway, and as a group they work best with no more than 75% of the disk filled with data. > Anyway, with this new alignment, my computer doesn't lock up for as > long. I'm still getting a few seconds here and there however. I have > a network switch that may be going bad - my brother in law couldn't > get it to work with his laptop, so maybe there's problem with it too. > What mount options do you have for your SSD mounted partitions? I vacilate on putting discard in mine, but currently I just have relatime for /, and relatime,user_xattr for /home. Discard will run the garbage collection when you modify files, but after I install updates and I'm ready to drop down to user I run 'fstrim -v /; fstrim -v /home; exit'. The lock up that you're describing sounds like garbage collection running. -- Efraim Flashner efraim.flashner@gmail.com 4096R/CA3D8351 created: 2013-10-08 GPG key = A28B F40C 3E55 1372 662D 14F7 41AA E7DC CA3D 8351
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